Reversible mechanochromic luminescence of phenothiazine-based 10,10′-bianthracene derivatives with different lengths of alkyl chains

Abstract

A series of 10,10 0 -bis(2-(N-alkylphenothiazine-3-yl)vinyl)-9,9 0 -bianthracene compounds (PVBAn, n ¼ 2, 8, 12 and 16) with different lengths of N-alkyl chains have been designed and synthesized to systematically investigate the effect of chain length on their solid-state fluorescence properties. The results showed that these compounds emitted strong fluorescence in solution and in the solid state. Their emission wavelengths were also strongly affected by solvent polarity, indicating intramolecular charge transfer (ICT) transitions. Interestingly, the fluorescence emission and grinding-induced spectral shifts of PVBAn solids are alkyl length-dependent. PVBA2 shows the smallest fluorescence and absorption spectrum shifts under mechanical force stimuli. Homologues with longer alkyl chains exhibit similar mechanochromic behaviors and larger fluorescence contrasts after grinding. Moreover, the fluorescence emission of ground solid PVBA16 can recover at room temperature, but other compounds need high temperatures for fluorescence to be restored. Differential scanning calorimetry experiments reveal that the cold-crystallization temperature difference is responsible for thermal restoration behaviors. This work demonstrates the feasibility of tuning the solid-state optical properties of fluorescent organic compounds by combining the simple alteration of chemical structure and the physical change of aggregate morphology under external stimuli.

Structural Features Guiding the Design of Liquid-Crystalline Elastomeric Fluorescent Force Sensors

“…It is also interesting to stress at this point that mechanochemical reactions can also be performed in polymeric matrixes containing carefully chosen mechanophores with an extremely high spatial precision, permitting 3D nanoprinting and the production of nanodevices and nanosensors for measuring mechanical stress in situ [32]. It should be also mentioned that non-polymeric materials, mainly crystalline solids, have also been proved to change their luminescence upon grinding, smearing, shearing, etc., due to drastic modifications of their crystalline structures [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51]. However, in many of these instances, the initial state of the system must be recovered either by recrystallization or by exposing the solid to vapors of a suitable solvent.…”

Side chain effects on the solid-state emission behaviours and mechano-fluorochromic activities of 10H-phenothiazinylbenzo[d]imidazoles

“…In literature, the cases with positive 8 or negative 9 or small side effects 10 have been reported. Occasionally, emission shis before and aer force application are rstly increased and then decreased, 11 or vice versa, 12 as alkyl chains are extended. Hence, for a given uorophore and its homologues, the side chain effect on their MFC performances is difficult to predict and should be investigated individually.…”

Novel Phenothiazine‐5‐oxide Based Push‐Pull Molecules: Synthesis and Fine‐Tuning of Electronic, Optical and Thermal Properties

“…Designing and fine‐tuning of push‐pull type organic materials have gained considerable attention in the past few years for their practical applications in the field of photovoltaic devices, optical electronic devices, non‐linear optical (NLO) switches,, dye sensitized solar cells (DSSCs), photosensitizers,, solvatochromic,, photochromic, piezochromic materials, etc. Small push‐pull molecules of different architecture such as D‐A, D‐A‐D, D‐ π ‐A, D‐ π ‐A‐ π ‐D, (D‐ π ‐) 2 A‐ π ‐D, D‐D‐ π ‐A, etc.…”